The present invention relates to a semiconductor laser device and semiconductor laser device manufacturing method.
Recently, AlGaInP-based red semiconductor laser devices capable of emitting light at a wavelength in a 600-nm band have been increasingly used as light sources of a pointer, a bar-code reader, a laser beam printer and optical disk devices, acquiring greater importance.
As a semiconductor laser device of this type, there has been one as shown in FIG. 7. This semiconductor laser device is a ridge stripe type, in which a ridge section formed of a p-type second clad layer 108, a p-type interlayer 109 and a p-type cap layer 110 is formed so as to be embedded in an n-type current constriction layer 113 and a p-type contact layer 116 by the MBE method.
The above-mentioned conventional semiconductor laser device is manufactured as follows. That is, as shown in FIG. 8A, an n-type GaAs buffer layer 102, an n-type GaInP buffer layer 103, an n-type AlGaInP clad layer 104, a GaInP/AlGaInP multiple quantum well active layer 105, a p-type first AlGaInP clad layer 106, a GaInP etching stop layer 107, a p-type second AlGaInP clad layer 108, a p-type GaInP interlayer 109 and a p-type GaAs cap layer 110 are successively grown by the MBE method on an n-type GaAs substrate 101 that has a plane, which is inclined at an angle of 15° toward the [011] direction from the (100) plane, as its principal plane.
Subsequently, an Al2O3 film 111 is vapor deposited on the p-type cap layer 110, and this Al2O3 film 111 is processed by patterning through photoetching into a stripe shape.
Subsequently, etching is carried out using a resist film 112, which has been used for the pattern processing of the Al2O3 film 111, as a mask to remove both side portions of the p-type second clad layer 108, the p-type interlayer 109, the p-type cap layer 110 and the Al2O3 film 111, forming a ridge section as shown in FIG. 8B.
Subsequently, the resist film 112 is removed, and thereafter, the Al2O3 film 111 is removed by etching. Then, second-time crystal growth is carried out by the MBE method, growing n-type AlInP on the GaInP etching stop layer 107 and the ridge section (FIG. 8C). At this time, a single-crystal AlInP layer 113, which becomes a current constriction layer, is formed on the GaInP etching stop layer 107, and a polycrystalline AlInP layer 114 is grown on the p-type cap layer 110 of the ridge section.
Subsequently, a resist is coated on the n-type AlInP current constriction layer 113 and the AlInP layer 114 by a spinner. At this time, a resist film 115 is formed on the n-type AlInP current constriction layer 113, whereas the resist film is scarcely formed on the polycrystalline AlInP layer 114.
Subsequently, the resist on the AlInP layer 114 is completely removed by O3-UV ashing, so that the resist film 115 is disposed only on the n-type AlInP current constriction layer 113 as shown in FIG. 9A.
Then, the polycrystalline AlInP layer 114 is removed by etching using the resist film 115 as a mask as shown in FIG. 9B.
Subsequently, the resist 115 is removed as shown in FIG. 9C.
Subsequently, a p-type GaAs contact layer 116 is formed through crystal growth by third-time MBE method, and electrodes 117 and 118 are formed on the upper surface of this p-type contact layer 116 and the lower surface of the n-type GaAs substrate 101, respectively, obtaining an AlGaInP-based red semiconductor laser device as shown in FIG. 7.
However, the above-mentioned semiconductor laser device manufacturing method has a problem that the n-type AlInP current constriction layer 113 located on both sides of the ridge section is excessively etched when the polycrystalline AlInP layer 114 is removed by etching during the process shown in FIG. 9B and the operating current value of the semiconductor laser device consequently increases.
This is ascribed to the fact that the portion formed on the side surfaces of the ridge section in the n-type AlInP current constriction layer 113 formed through the process shown in FIG. 8C has a crystal structure more prone to etching than the portion formed on the GaInP etching stop layer 107. The portion of the n-type AlInP layer 113, which is formed on the side surfaces of the ridge section and is brought in contact with the AlInP layer 114, is etched by the etchant used when the polycrystalline AlInP layer 114 is removed by etching. As a result, over-etching occurs in the portions located on the side surfaces of the ridge section in the n-type AlInP current constriction layer 113. P-type GaAs enters these over-etched portions during third-time crystal growth by the MBE method. Since this GaAs absorbs light generated in the active layer, the light confinement effect of the ridge section is reduced, and external differential quantum efficiency is reduced, disadvantageously increasing a threshold current value and an operating current value.